I had no symptoms of stopping zoloft, (sertraline) but about two weeks afterwards I began nuvaring. I am now experiencing anxiety and moodiness. Due to which?

MAYBE BOTH. It may be a combination of both. Not sure what dosage the zoloft (sertraline) was but there could be some withdrawal or even reemergence of symptoms. Also there can be mood changes with hormones like with the nuva ring. Check with you gynecologist as well as the physician that prescribed the zoloft (sertraline).